Efficient Forced Air Heater

ABSTRACT

Provided is a forced air heater. The forced air heater may comprise a housing defining a duct. The duct may be adapted for a flow of fluid therethrough. The heater may be adapted to provide a flow of fluid through the duct that is substantially laminar or transient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/354,954, filed Jun. 15, 2010. All of the subject matter disclosed by U.S. Provisional Application No. 61/354,954 is hereby incorporated by reference into this application.

TECHNICAL FIELD

Certain embodiments disclosed herein relate generally to heaters. More specifically, certain embodiment disclosed herein related generally to forced air heaters. More specifically, certain embodiment disclosed herein related generally to the efficiency of forced air heaters.

BACKGROUND

Heaters provide heat. Some heaters combust a fuel in air to provide heat. Forced air heaters are heaters that combust a fuel in air to provide heat and which provide a forced air output through an output opening.

In some embodiments, forced air heaters comprise design elements that are inefficient in one or more ways. In some embodiments forced air heaters are subject to a problem wherein wind or strong currents in ambient air to blow into an output opening and counter to the air output. Wind resistance is the resistance of a forced air heater to wind or strong currents in ambient air blowing into an output opening and counter to the air output.

Some forced air heater comprise components adapted to promote wind resistance. Many components adapted to promote wind resistance decrease the efficiency of the forced air heater.

Some forced air heater comprise components adapted to promote the mixture of air and fuel. Many components adapted to promote the mixture of air and fuel decrease the efficiency of the forced air heater.

In some embodiments, inefficiency manifests itself as noise or resistance to air flow through the heater.

It remains desirable to provide forced air heaters with improved efficiency, but which comprise components adapted to promote wind resistance, or adapted to promote the mixture of air and fuel, or both.

SUMMARY

Provided is a forced air heater. The forced air heater may comprise a housing defining a duct. The duct may be adapted for a flow of fluid therethrough. The heater may be adapted to provide a flow of fluid through the duct that is substantially laminar or transient.

Further provided is a forced air heater. The forced air heater may comprise a housing defining a duct. The duct may be adapted for a flow of fluid therethrough. The heater may be adapted to provide a flow of fluid through the duct where the flow of fluid has a Reynolds Number less than 4000.

Further provided is a forced air heater. The forced air heater may comprise a housing defining an elongated interior region. The elongated interior region may have a relative roughness less than 0.05. The elongated interior region may have a first end and second end. The housing may comprise a first opening proximate to the first end and adapted to provide fluid communication therethrough between the environment and the interior region. The housing may comprise a second opening proximate to the second end and adapted to provide fluid communication therethrough between the environment and the interior region. The forced air heater may comprise an air movement device adapted to create an air flow into the first opening and a flow of fluid out of the second opening. The heater may be adapted to produce a fully developed flow of fluid therethrough without producing sound of more than 60 db.

Further provided is a forced air heater. The forced air heater may comprise a housing defining an elongated interior region. The elongated interior region may have a relative roughness less than 0.05. The elongated interior region may have a first end and second end. The housing may comprise a first opening proximate to the first end and adapted to provide fluid communication therethrough between the environment and the interior region. The housing may comprise a second opening proximate to the second end and adapted to provide fluid communication therethrough between the environment and the interior region. The second opening may have an area of less than 0.008 square meters. The forced air heater may comprise an air movement device adapted to create an air flow into the first opening and a flow of fluid out of the second opening where the flow of fluid exceeds 0.005 kg/s. The forced air heater may be adapted to produce a fully developed flow of fluid therefrom having a Reynolds Number less than 4000. The forced air heater may be adapted to produce a fully developed flow of fluid therefrom without producing sound of more than 60 db.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a heater;

FIG. 2 is another cross-sectional view of a heater;

FIG. 3 is a cross-sectional view of another heater;

FIG. 4 is a Moody diagram;

FIG. 5 is a view of a baffle; and

FIG. 6 is view of another baffle.

DETAILED DESCRIPTION

Reference will be made to the drawings, FIGS. 1-6, wherein the showings are only for purposes of illustrating certain embodiments of an efficient forced air heater, and not for purposes of limiting the same.

In certain embodiments, a forced air heater 50 may comprise a housing 100, a burner 150, and an air movement device 160.

A housing 100 may define an interior region 120 adapted to accept a flow of input air 210, a flow of fuel 220, or a flow of a mixture of air 200 and fuel 220; adapted to contain combustion of air 200 and fuel 220, and adapted to output a flow of heat 260 and combustion products 280. Air 200 within the housing 200 may be drawn from input air 210 or from another source or inlet. In certain embodiments, the housing 100 may be a hollow elongated structure defining an interior region 120 therein. The housing 100 may comprise a first end 102 and a second end 104. The first end 102 may comprise an inlet opening 106 adapted to provide fluid communication therethrough between the environment 90 and the interior region 120. The second end 104 may comprise an outlet opening 108 adapted to provide fluid communication therethrough between the environment 90 and the interior region.

In certain embodiments, and without limitation, the housing 100 may form a duct 110 defining an elongated interior region 120, a first end 102 and a second end 104, an inlet opening 106, and an outlet opening 108. In certain embodiments, and without limitation, a duct 110 is adapted to permit the flow of therethrough of a fluid, such as without limitation, air 200, or a mixture of air 200 and fuel 220, or combustion products 280.

In certain embodiments, and without limitation, an outlet opening 108 may have an area less than 0.2 square meters. In certain embodiments, and without limitation, an outlet opening 108 may have an area less than 0.1 square meters. In certain embodiments, and without limitation, an outlet opening 108 may have an area less than 0.05 square meters.

An interior region 120 or a duct 110 may be defined by an interior surface 115 of a housing 100. An interior region 120 or a duct 110 may be shaped as a box, a prism, a cylinder, or some other shape. A cylindrical shaped duct 110 may also be considered a pipe. An interior region 120 or duct 110 may have some definable roughness as the term is used in FIG. 4.

In certain embodiments the housing 100 is adapted for operation wherein input air 210 flows into the first end 102 of housing 100; wherein air 200 is mixed with either fuel 220 or a mixture of air 200 and fuel 220 to form a mixture of air 200 and fuel 220; wherein the mixture is combusted to produce heat 260 and combustion products 280; and wherein the heat 260 and combustion products 280 flow out of the second end 104 of the housing 100.

In certain embodiments, and without limitations, a forced air heater 50 may be adapted to operate in a manner that permits some fraction of the input air 210 that flows into the first end 102 of housing 100 not to participate in the combustion reaction and to flow out of the second end 104 of the housing 100 as output air 290. In certain embodiments, in operation, some fraction of the air 200 that flows into the first end 102 of housing 100 does not participate in the combustion reaction and flows out of the second end 104 of the housing 100 as output air 290. In certain embodiments, the fraction of the air 200 that flows out of the second end 104 of the housing 100 as output air 290 is heated by heat 260 such that the temperature of output air 290 is higher than that of the input air 210 and may be used to convey heat to the environment 90 or to other regions or objects.

In certain embodiments, and without limitations, a burner 150 may comprise a site for combustion of a mixture of air 200 and fuel 220 to yield heat 260 and combustion products 280. A fuel 220 may comprise kerosene, propane, natural gas, alcohol, mixtures thereof, or other fuels. In certain embodiments, and without limitations, burner 150 may be supplied with air 200 supplied from the input air 210. In certain embodiments, and without limitations, burner 150 may be supplied with fuel 220 or a mixture of air 200 and fuel 220. In certain embodiments, and without limitations, a burner 150 may be supplied with fuel 220 or a combustion a mixture of air 200 and fuel 220 transported to the burner 150 by a pipe 152, hose, conduit, or other fluid conveyance. Fuel 220 may be supplied to the forced air heater 50 by an associated fuel tank, an associated fuel bottle, an associated supply line, or other associated fuel container or source.

An air movement device 160 may comprise any device capable of intaking ambient air and providing air flow therefrom. In certain embodiments, and without limitations, an air movement device 160 may comprise an axial fan 160, a centrifugal fan, a crossflow fan, another type of fan, a blower, an air compressor, a pump, or some combination thereof. In certain embodiments, and without limitations, an air movement device is adapted to establish an input air flow and output air flow where the output air flow has substantially higher head than does the input air flow. In certain embodiments, and without limitation, an air movement device 160 may be engaged with the housing 100 so as to be partially or fully encompassed by the housing 100. In certain embodiments, and without limitation, an air movement device 160 may be engaged with the housing so as to be filly encompassed by an interior region 120 or duct 110. In certain embodiments, and without limitation, an air movement device 160 may produce air flow through the forced air heater 50 defined by a linear flow rate, a volumetric flow rate, a mass flow rate, or some other flow criteria. In certain embodiments, and without limitation, air flow may be defined by a linear flow rate within the range of 0 to 50 meters per second. In certain embodiments, and without limitation, air flow may be defined by a volumetric flow rate within the range of 0 to 0.4 cubic meters per second. In certain embodiments, and without limitation, air flow may be defined by a volumetric flow rate within the range of 0 to 0.5 kilograms per second.

In certain embodiments, and without limitation, an air movement device 160 may drive an air flow through the forced air heater 50 which is adapted to impart substantially similar flow to other materials or fluids such as fuel 220, combustion products 280, output air 290, or other fluids.

A forced air heater 50 may comprise a baffle 300. A baffle 300 may comprise a mesh, a burner plate, a screen, a flameholder plate, or other perforated surface or perforated plate. A baffle 300 may be substantially flat, may be substantially frustoconical, or may comprise other geometries. A baffle 300 may comprise closed regions 320 and open regions 340. Closed regions 320 are substantially impervious to the flow of air 200 or fuel 220 therethrough. As will be developed further herebelow, closed regions 320 are substantially impervious to the flow of wind or air currents therethrough. Open regions 340 are substantially open to the flow of air 200 or fuel 220 therethrough. As will be developed further herebelow, open regions 340 are substantially open to the flow of wind or air currents therethrough. In some embodiments, and without limitation, as shown in FIGS. 2 and 3, open regions 320 may be defined by perforations 310. Perforations 310 may be round, diamond-shaped, or any other shape.

In some embodiments, and without limitation, a baffle 300 may be a substantially closed baffle 300. A substantially closed baffle 300 may comprise substantially more closed regions 320 than open regions 340. In some embodiments, and without limitation, as shown in FIG. 2, a substantially closed baffle 300, may comprise a baffle 300 wherein the fraction of the area of the baffle defined by closed regions 320 is substantially greater than the fraction of the area of the baffle defined by open regions 340.

The percentage of closure is the fraction of the area of the baffle defined by closed regions 320. In certain embodiments, and without limitation, a substantially closed baffle 300 may be 60% closed, 70% closed, 80% closed, 90% closed, 95% closed, or some other percentage closed.

In some embodiments, and without limitation, a baffle 300 may be a substantially open baffle 300. A substantially open baffle 300 may comprise substantially more open regions 340 than closed regions 320. In some embodiments, and without limitation, as shown in FIG. 3, a substantially open baffle 300, may comprise a baffle 300 wherein the fraction of the area of the baffle defined by open regions 340 is substantially greater than the fraction of the area of the baffle defined by closed regions 320.

In certain embodiments, and without limitation, a substantially open baffle 300 may be 40% closed, 30% closed, 20% closed, 10% closed, 5% closed, or some other percentage closed.

The percentage of closure of a baffle 300, may substantially influence the flow properties of air 200 fuel 220 or other fluids flowing therethrough. In some embodiments, and without limitation, increasing the closure of baffle 300 may increase the resistance to fluid flow therethrough of the interior region 120, or the duct 110, or the forced air heater 50. In some embodiments, and without limitation, increasing the closure of baffle 300 may increase the friction factor or the relative roughness of the interior region 120 or the duct 110. In some embodiments, and without limitation, a more closed baffle 300 may promote greater turbulence of a fluid flowing therethrough than would a more open baffle 300. By contrast, more open baffle 300 may promote greater laminar flow of a fluid flowing therethrough than would a more closed baffle 300.

In certain embodiments, open regions 340 or perforations 310 may define apertures through which air 200 or fuel 220 or other fluids may flow. In certain embodiments, and without limitation, open regions 340 or perforations 310 may be adapted to produce choked flow therethrough.

As shown in FIG. 4, flow may be laminar, turbulent, or in a transition state between laminar and turbulent flow. As referenced above, the flow properties of a fluid in a forced air heater 50 may include the nature of the flow with respect to whether the flow is laminar, turbulent, or transient. Transient flow is in a transition state between laminar and turbulent flow. The Reynolds Number, Re, can be used to determine if flow is laminar, transient or turbulent. In certain embodiments, and without limitation, flow is laminar when Re is less than about 2300; flow is transient when Re is between about 2300 and 4000; and flow is turbulent when Re is greater than about 4000. As will be discussed further below, there are advantages to both laminar and turbulent flow conditions.

In certain embodiments, a forced air heater 50 may be adapted to operate in conditions comprising substantial wind or strong air currents. In some embodiments, wind or strong air currents may reverse the direction of flow created by the air movement device 160 within the forced air heater 50, or may blow heat 260 or combustion products 280 into the forced air heater 50, or may otherwise produce undesired operation of the forced air heater 50. A forced air heater 50 may comprise adaptations to prevent wind or strong air currents from reversing the flow within the forced air heater 50, or from blowing heat 260 or combustion products 280 into the forced air heater 50, or from otherwise producing undesired operation of the forced air heater 50. Adaptations to prevent wind or strong air currents from reversing the flow within the forced air heater 50, or from blowing heat 260 or combustion products 280 into the forced air heater 50, or from otherwise producing undesired operation of the forced air heater 50 are adaptations to promote wind resistance.

Without limitation, in certain embodiments, an adaptation that a forced air heater may comprise that promotes wind resistance is a substantially closed baffle 300. As noted above, in some embodiments, and without limitation, increasing the closure of baffle 300 may increase the resistance of the interior region 120, or the duct 110, or the forced air heater 50, to flow therethrough. The percentage of closure of a substantially closed baffle 300 may be chosen to increase the resistance of the interior region 120, or the duct 110, or the forced air heater 50, to flow therethrough and thereby to increase the wind resistance. In some embodiments, and without limitation, as the percentage of closure of the baffle 300 increases, wind resistance increases.

Without limitation, in certain embodiments, an adaptation that a forced air heater may comprise that promote wind resistance is a diffuser 400. A diffuser is a conduit comprising a first opening 410 and a second opening 420, where the area of the second opening 420 is greater than the area of the first opening 410. In certain embodiments, the first opening 410 of the diffuser 400 is adapted to receive flow from the air movement device 160. In certain embodiments, the first opening 410 of the diffuser 400 may be closely engaged with the outlet of the air movement device 160 so that the first opening 410 of the diffuser 400 is adapted to receive substantially all of the flow from the air movement device 160. In certain embodiments, the diffuser is adapted to receive flow from the air movement device 160 through first opening 410 and for the flow to exit the diffuser 400 through second opening 420. In certain embodiments, the diffuser comprises only two openings, first opening 410 and second opening 420. In certain embodiments, the second opening 420 of the diffuser 400 may be closely engaged with the interior surface 115 of the housing 100. In certain embodiments, a diffuser 400 may be hollow and substantially frustoconical.

Without limitation, in certain embodiments, an adaptation that a forced air heater may comprise that promote wind resistance is a stagnation fitting 430. A stagnation fitting 430 is a plate, block, or other geometry that is impervious to flow. In certain embodiments, a stagnation fitting 430 is placed along the axis of a hollow and substantially frustum-shaped diffuser 400. In certain embodiments, a stagnation fitting 430 is placed proximate to the axis of revolution of an air movement device 160 comprising an axial fan. In certain embodiments, a stagnation fitting 430 is a circular plate placed proximate to the axis of revolution of an axial fan.

Without limitation, in certain embodiments, a forced air heater 50 that comprises certain adaptations, such as a diffuser 400, or a stagnation fitting 430, or both, to promote wind resistance, may not require other adaptations, such as a substantially closed baffle 300, to provide a desired level of wind resistance.

In certain embodiments, a forced air heater 50 may be adapted to promote the mixing of air 200 and fuel 220. Without limitation, in certain embodiments, an adaptation that a forced air heater may comprise that promotes the mixing of air 200 and fuel 220 is a substantially closed baffle 300. As noted above, in some embodiments, a more closed baffle 300 may promote greater turbulence of a fluid flowing therethrough than would a more open baffle 300. In certain embodiments, a forced air heater 50 may comprise a substantially closed baffle 300 that is adapted to promote greater turbulence of air 200 and fuel 220 flowing therethrough. Without limitation, turbulence may promote mixing action. In certain embodiments, a forced air heater 50 may comprise a substantially closed baffle 300 that is adapted to promote greater turbulence of air 200 and fuel 220 flowing therethrough and, thereby, promote the mixing of air 200 and fuel 220.

Without limitation, in certain embodiments, an adaptation that a forced air heater may comprise that promotes the mixing of air 200 and fuel 220 is a venturi 500. A venturi 500 is a device that mixes air and fuel. In certain embodiments, a venturi 500 may comprise an orifice (not shown) adapted to introduce a fuel 220 from an associated fuel source (not shown), an inlet aperture 520 adapted to introduce air, and an outlet (not shown) adapted to output a mixture of the fuel 220 and air 200.

Without limitation, in certain embodiments, a forced air heater 50 that comprises certain adaptations, such as a venturi 500, to promote the mixing of air 200 and fuel 220, may not require other adaptations, such as a substantially closed baffle 300, to provide a desired level of mixing of air 200 and fuel 220.

In addition to the above described benefits, in certain embodiments, turbulent flow may also cause, or be correlated with other operational conditions. Without limitation, in certain embodiments, turbulent flow may cause or be correlated with the formation of eddies, vortices, or other complex flow patterns, increased drag, increased noise, increased inefficiency or some combination thereof. Without limitation, in certain embodiments, a substantially closed baffle 300 may promote both turbulence and inefficiency in the form of resistance to air flow through the heater. Without limitation, in certain embodiments, a substantially closed baffle 300 may promote both turbulence and noise stemming directly or indirectly from turbulent flow.

Turbulent flow may be substantially louder or noisier than laminar or transient flow. Without limitation, in certain embodiments, a forced air heater 50 operating with substantially turbulent flow therethrough may produce noise in excess of 50 db, noise in excess of 60 db, noise in excess of 70 db, or noise in excess of 80 db. Without limitation, in certain embodiments, a forced air heater 50 operating without substantially turbulent flow therethrough may not produce noise in excess of 60 db, may not produce noise in excess of 50 db, may not produce noise in excess of 40 db, or may not produce noise in excess of 30 db.

Turbulent flow may be substantially less efficient than laminar or transient flow. Without limitation, in certain embodiments, a forced air heater 50 operating with substantially turbulent flow therethrough may require substantially greater power than an otherwise similar forced air heater 50 operating with substantially laminar or transient flow in order to produce a substantially a similar rate of output flow. Without limitation, in certain embodiments, a forced air heater 50 operating without substantially turbulent flow therethrough may require 10% more power, 20% more power, 30% more power, 40% more power, 50% more power, 60% more power, 70% more power, or 80% more power than an otherwise similar forced air heater 50 operating with substantially laminar or transient flow in order to produce a substantially a similar rate of output flow.

Without limitation, in certain embodiments, a forced air heater 50 may comprise substantially open baffle 300. In certain embodiments, and without limitation, a forced air heater 50 comprising a substantially open baffle 300 may comprise a diffuser 400 or a stagnation fitting 430, or both to promote wind resistance. In certain embodiments, and without limitation, a forced air heater 50 comprising a substantially open baffle 300 may comprise a venturi 500 to promote the mixing of air 200 and fuel 220. In certain embodiments, and without limitation, a forced air heater 50 may comprise a substantially open baffle 300, a diffuser 400, a stagnation fitting 430, and a venturi 500.

In certain embodiments, and without limitation, a forced air heater 50 that operates in a manner that avoids or does not promote substantial turbulent air flow may benefit from non-turbulent flow that may be quieter and more efficient for lack of some of the drag and noise of turbulent flow. In certain embodiments, and without limitation, a forced air heater 50 may be adapted to operate in a manner that avoids or does not promote substantial turbulent air flow. In certain embodiments, and without limitation, a forced air heater 50 adapted to operate in a manner that avoids or does not promote substantial turbulent air flow may operate in a manner such that flow therethrough is substantially laminar, or such that flow therethrough is substantially transient. A forced air heater 50 adapted to operate in a manner that avoids or does not promote substantial turbulent air flow may comprise a diffuser 400 or a stagnation fitting 430, or both to promote wind resistance. A forced air heater 50 adapted to operate in a manner that avoids or does not promote substantial turbulent air flow may comprise a venturi 500 to promote the mixing of air 200 and fuel 220. A forced air heater 50 adapted to operate in a manner that avoids or does not promote substantial turbulent air flow may not comprise a substantially closed baffle 300. A forced air heater 50 adapted to operate in a manner that avoids or does not promote substantial turbulent air flow may comprise an air movement device 160 adapted to use a relatively small amount of power and still be adapted to produce an output flow rate substantially similar to that of an otherwise similar forced air heater 50 adapted to operate in a manner that promotes substantial turbulent air flow.

While the efficient forced air heater has been described above in connection with the certain embodiments, it is to be understood that other embodiments may be used or modifications and additions may be made to the described embodiments for performing the same function of the efficient forced air heater without deviating therefrom. Further, efficient forced air heater may include embodiments disclosed but not described in exacting detail. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments may be combined to provide the desired characteristics. Variations can be made by one having ordinary skill in the art without departing from the spirit and scope of efficient forced air heater. Therefore, the efficient forced air heater should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the attached claims. 

1. A forced air heater comprising, a housing defining a duct, said duct adapted for a flow of fluid therethrough; said heater adapted to provide a flow of fluid through the duct that is substantially laminar or transient.
 2. The forced air heater of claim 1, wherein said flow of fluid comprises air, fuel, combustion products, or some combination thereof.
 3. The forced air heater of claim 2, wherein said flow of fluid has a velocity exceeding 0.2 m/s.
 4. The forced air heater of claim 3, wherein said flow of fluid has a velocity exceeding 0.4 m/s.
 5. The forced air heater of claim 1, wherein said flow of fluid is substantially laminar.
 6. The forced air heater of claim 5, wherein said flow of fluid comprises air, fuel, combustion products, or some combination thereof.
 7. The forced air heater of claim 6, wherein said flow of fluid has a velocity exceeding 0.2 m/s.
 8. The forced air heater of claim 7, wherein said flow of fluid has a velocity exceeding 0.4 m/s.
 9. A forced air heater comprising, a housing defining a duct, said duct adapted for a flow of fluid therethrough; said heater adapted to provide a flow of fluid through the duct where said flow of fluid has a Reynolds Number less than
 4000. 10. The forced air heater of claim 9, wherein said flow of fluid comprises air, fuel, combustion products, or some combination thereof.
 11. The forced air heater of claim 10, wherein said flow of fluid exceeds 0.002 kg/s.
 12. The forced air heater of claim 11, wherein said flow of fluid exceeds 0.005 kg/s.
 13. The forced air heater of claim 9, wherein said flow of fluid has a Reynolds Number less than
 2300. 14. The forced air heater of claim 13, wherein said flow of fluid comprises air, fuel, combustion products, or some combination thereof.
 15. The forced air heater of claim 14, wherein said flow of fluid exceeds 0.002 kg/s.
 16. The forced air heater of claim 11, wherein said flow of fluid exceeds 0.005 kg/s.
 17. A forced air heater comprising, a housing defining an elongated interior region, said elongated interior region having a relative roughness less than 0.05, said elongated interior region having a first end and second end, said housing comprising, a first opening proximate to the first end and adapted to provide fluid communication therethrough between the environment and the interior region, a second opening proximate to the second end and adapted to provide fluid communication therethrough between the environment and the interior region, an air movement device adapted to create an air flow into the first opening and a flow of fluid out of the second opening; and wherein, the heater is adapted to produce a fully developed flow of fluid therethrough without producing sound of more than 60 db.
 18. The forced air heater of claim 17, wherein the heater is adapted to produce a fully developed air flow therethrough without producing sound of more than 45 db.
 19. The forced air heater of claim 18, wherein the heater is adapted to produce a fully developed air flow therethrough without producing sound of more than 30 db.
 20. A forced air heater comprising, a housing defining an elongated interior region, said elongated interior region having a relative roughness less than 0.05, said elongated interior region having a first end and second end, said housing comprising, a first opening proximate to the first end and adapted to provide fluid communication therethrough between the environment and the interior region, a second opening proximate to the second end, adapted to provide fluid communication therethrough between the environment and the interior region, and having an area of less than 0.008 square meters; an air movement device adapted to create an air flow into the first opening and a flow of fluid out of the second opening, said flow of fluid exceeding 0.005 kg/s; and wherein, the heater is adapted to produce a fully developed flow of fluid therefrom having a Reynolds Number less than 4000; and wherein the heater is adapted to produce a fully developed flow of fluid therefrom without producing sound of more than 60 db. 